Wireless communication systems are widely deployed to provide various communication services, such as: voice, video, packet data, circuit-switched info, broadcast, messaging services, and so on. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, etc.). These systems can be multiple-access systems that are capable of supporting communication for multiple terminals by sharing available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, and so on.
In LTE, any data transmission requires that the smartphone is in ‘high power’ Radio Resource Control (RRC) connected state. With all data applications there are often short moments when no data is sent or received and during those moments connected state discontinuous reception (DRX) can save energy. Connected state DRX (C-DRX) cyclically wakes up and shuts down the receiver circuits in order to save energy.
In LTE, C-DRX allows the user equipment (UE) to periodically sleep and not continuously decode the physical downlink control channel (PDCCH) and the physical downlink shared channel (PDSCH). Similarly, for VoLTE type of applications, the enhanced Node B (eNB) can allocate resources in a semi-persistent scheduling fashion (SPS). Those resources are available periodically and no additional signaling is required. This is particularly useful for applications such as voice.
In cellular systems and 3GPP, a Hybrid Automatic Repeat Request (HARQ), which is a combination of forward error coding (FEC) and retransmission mechanism, is used to obtain data communication reliability. As per current 3GPP specifications, in case of uplink (UL) HARQ, the UE needs to stay awake in order to monitor PHICH for all configured retransmissions. The HARQ is then breaking the C-DRX cycle/pattern of ON/OFF period of time, which is impacting the battery life of an UE.
In the current 3GPP standards, in the case where the UE receives an ACK in PHICH, the UE will keep the data in the HARQ buffer. The UE will flush the HARQ buffer only if the maximum number of transmissions has been reached (i.e., an ACK alone is not sufficient to flush the HARQ buffer). Even in the case of C-DRX, the UE has to monitor all the PDCCH opportunities for the number of HARQ transmissions that are configured (e.g., 4 or 5). Even in good conditions, after the UE receives an ACK, the UE is required to stay awake till all possible PDCCH opportunities corresponding to the potential HARQ transmission have been monitored which increases UE wake time and hence reduce the UE's battery life.
Therefore, there is a need for techniques to avoid staying awake when it is not necessary.